Charge air coolers of what is referred to as packet design are used in particular in large engines where the charge air is cooled by a liquid coolant. These charge air coolers are produced and brazed in a design made totally from aluminum, the cooler block of cuboidal design and the associated connecting branches for the charge air and the coolant being produced separately. The cooler block comprises a multiplicity of plates which are layered on one another and between which strips for forming flow passages and for spacing are arranged. The ready stacked block is then brazed in a brazing furnace. The flow passages for the charge air have corrugated fins or turbulence inserts in the interior, in order to improve the transfer of heat and to increase the internal compressive strength. The cooling passages have a smaller flow cross section than the charge air passages and are bounded by intermediate strips and outer terminating strips. The transfer of heat between coolant and charge air takes place in cross current, i.e. the coolant passages and charge air passages run perpendicularly to one another. A charge air cooler of this type has been disclosed by the applicant in DE-A 196 51 625 mentioned above. In the case of the known charge air cooler, the cooling passages for the liquid coolant have a rectangular cross section, since the intermediate strips arranged between the adjacent plates likewise have a rectangular cross section. A problem with these heat exchangers are the unsteady states, in particular on the charge air side, which, due to sharp changes in temperature with high temperature differences and temperature peaks, lead to the coolant overheating, i.e. to the boiling point being exceeded locally with steam bubbles being formed. It is absolutely to be avoided.
A similar heat exchanger of packet design, likewise a charge air cooler, has been disclosed by the applicant in DE-C 196 44 586. The difference in this case are the cooling passages which are formed by a plate-like extruded profile. The passage cross sections are rectangular or oval, but this is primarily for manufacturing reasons (extrusion).